<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        /* 标签选择器 标签名{样式} */
        div{
            width: 100px;
            height: 100px;
            background-color: burlywood;
        }
        /* 类选择器 class 在调用的时候用 */
        .two{
            background-color: cornsilk;
        }
        .double{
            width: 30px;
        }
#three{
    background-color: darkgray;
}
    </style>
</head>
<body>
    <div class="two"></div> 
    <div class="two double"></div>
<!-- id选择器  用#调用 -->
    <div id="three"></div>
</body>
</html>